The practice of carrying a wish-in-scribed document for successful voyage is common in Bengal.
The location of Raktamrttika on the Bhagirathi, the channel of the Ganges linking up to the port of Tamralipti, the gateway to Southeast Asia adds to the possibility of Mahanavika Buddhagupta hailing from Bengal.
The tone and support language and script of the inscription would rather place Buddhagupta to India and possibly Bengal.
An additional argument in favour of Bengal is that the names ending in Gupta are very common in Eastern India rather than anywhere else.